1. Field of the Invention
This invention relates to a fuel cell power generation system for generating electric power by using a hydrogen-rich reformed gas as fuel, to a method for operating same and, more particularly, to a method of operation when power generation is suspended.
2. Description of the Related Art
A fuel cell power generation system including a hydrogen-air fuel cell and a fuel gas generating apparatus (i.e., steam reformer+shifter) generally contains residual reformed gas (H.sub.2 -rich reformed gas) in the fuel cell and steam reformer after stopping feed of the H.sub.2 -rich reformed gas and air into the fuel cell upon suspending power generation. If the fuel cell, the associated apparatus or/and reformed gas connections leak reformed gas, the residual reformed gas will create a danger of explosion when mixed with air supplied anew in resuming operation of the system.
Further, if the above-mentioned residual reformed gas is allowed to remain the fuel-generating apparatus, the reforming catalyst therein will deteriorate because of carbon deposition by catalytic reforming at a low temperature. The fuel cell would also suffer a deleterious effect because its battery electric potential would not be lowered due to the presence of the above-mentioned residual reformed gas.
Japanese Kokai No. Hei 4-51469 discloses that, conventionally, after interrupting feed of air and reformed gas with suspension of fuel cell power generation, safety upon resuming operation of the system and satisfactory performance of the fuel-generating apparatus and the fuel cell can be achieved by forcibly purging the residual reformed gas with an external supply of inert gas such as nitrogen. However, the prior art approach utilizing inert gas requires a gas supply such as a nitrogen gas cylinder, which increase the size of the overall system and requires maintenance to exchange the consumed cylinder with a new one, so that such an approach is not suitable for a fuel cell power generation system mounted in, for example, an electric vehicle. Another disadvantage is the increase in cost of power generation due to the expense of the inert gas.